The present invention relates to an improved vortex flow meter for measuring the velocity and flow rate of a fluid flowing through a conduit by sensing a delicate pressure variation caused by a vortex train, which a buffle body disposed in the conduit sheds on the movement of the fluid past the buffle body, and converting the sensed pressure variation into an electric signal by means of a piezoelectric element or the like.
An example of vortex flow meters of the type described is disclosed in Japanese Utility Model Publication No. 46-21501/1971. This prior art vortex flow meter includes a strain gauge or like displacement sensor mounted on a membrane such as a diaphragm, so that a displacement sensed by the sensor is transformed into an electric signal. Such a flow meter construction, however, suffers from various drawbacks as enumerated below due to the inherent location of the sensor inside a narrow space formed in a bluff body.
(1) The flow meter cannot be manufactured, machined or assembled with ease due to the intricacy of construction.
(2) A large displacement cannot be sensed on account of the limited space available for the displacement of the sensor, whereby the sensitivity attainable with the flow meter is poor.
(3) The sensor is arranged to remain in direct contact with the fluid flowing through the conduit and, therefore, it is apt to be damaged to shorten the service life thereof.
(4) Any externally derived vibration is imparted to the sensor by way of the conduit or leads which are connected to the sensor. The external vibration is introduced as noise into a pressure variation component resulted from the vortex train, thereby noticeably lowering the sensing accuracy.